To detect angular velocity, various methods are practically used conventionally. Among them, as an angular velocity sensor which has a relatively simple structure and, moreover, is cheap, there is a widely used angular velocity sensor employing a method of detecting angular velocity by detecting, by some method, a Coriolis force generated in the direction orthogonal to the vibration direction when the angular velocity is applied to the vibrator in a one-dimensional vibrational motion state. The angular velocity sensor is also called a rate gyro. In particular, the angular velocity sensor using the vibrator is generally called a vibration gyro. In the vibration gyro, in many cases, a vibrator is made by using piezoelectric ceramics and, when angular velocity is applied to the vibrator excited by applying AC voltage, a displacement which occurs in the vibrator by the Coriolis force is extracted as an electric signal by the piezoelectric effect, and angular velocity is detected.
However, the piezoelectric angular velocity sensor using the piezoelectric ceramics has the following problems. Specifically, the angular velocity sensor has to employ either the configuration of adhering a piezoelectric element to a vibrator or the configuration of using a piezoelectric element as the vibrator itself In any of the cases employed, to drive the piezoelectric element and detect an electric signal by the piezoelectric effect, a wire has to be connected to an electrode of the piezoelectric element. As a result, external vibration is transmitted to the vibrator via the wire, and a problem occurs such that the angular velocity cannot be detected accurately.
To solve the problem, for example, in a vibration gyro (10) described in Japanese Patent Laid-open No. Hei 5-1917, as shown in FIG. 1 of the publication, a vibrator (12) is supported by supporters (22a and 22b) attached near a node point. As shown in FIG. 2 in the publication, lead wires (24a and 24b) are wound around the supporter 22b along the vibrator (12). Further, the lead wires (24a and 24b) are attached to the vibrator (12) by an elastic adhesive (26) such as silicone from the supporter (22b) to a portion near piezoelectric elements (14a, 14b). Similarly, a lead wire (24c) is partially adhered by the elastic adhesive (26) along the vibrator (12) and is wound around the supporter (22a). With the configuration, in the vibration gyro (10), the lead wires (24a to 24c) are attached to the vibrator (12) by using the elastic adhesive (26), so that the elastic adhesive (26) functions as a dumping material. Therefore, external vibration transmitted to the lead wires (24a to 24c) is damped (reduced) by the elastic adhesive (2b) and, as a result, the influence of the external vibration on vending mode vibration of the vibrator (12) is lessened.
In the vibration gyro (10), however, since the dumping characteristic changes according to the amount of the elastic adhesive (26), it is difficult to make the degree of lessening the external vibration constant (reproducibility is not excellent). Consequently, a problem exists such that it is difficult to detect the angular velocity with high precision. The elastic characteristic of the elastic adhesive (26) changes (deteriorates) due to temperature change or change with time. Therefore, the vibration gyro (10) also has a problem that it is difficult to excellently reduce leakage of vibration for long period. It is not easy to manage the elastic adhesive (26) and, moreover, workability of the elastic adhesive (26) is low. There is consequently a problem that it is also difficult to improve productivity of the vibration gyro (10).
As a method capable of more effectively reducing the influence on the vibrator of external vibration, a vibration gyro in which the vibrator is vibrated in a vibration mode which is hardly set for the vibrator by the external vibration is proposed. As a vibration gyro of this kind, for example, a gyro (gyroscope) disclosed in Japanese Patent Laid-open No. Hei 10-267667 is known. In this gyro, a ring-shaped vibration resonator (1) is suspended in magnetostatic field by a plurality of flexible supporting beams (5), and a vibration mode of vibrating the vibration resonator (1) by electromagnetic induction so that the shape can be changed from a ring shape to an oval shape or from the oval shape to the ring shape is used. Since the vibration mode is hardly set by external vibration, in the structure, even when external vibration is added, the influence on the vibration mode is extremely small. Therefore, in the gyro, also in the case where the external vibration is added, the angular velocity can be detected with high precision.
The gyro has, however, a problem that the plurality of flexible supporting beams (5) supporting the vibration resonator (1) have to be manufactured with high precision by using, for example, micromachining, so that the manufacturing cost is high.
On the other hand, in the angular velocity sensor disclosed in Japanese Patent Laid-open No. Hei 7-20140, excitation generated by a drive coil (12) is given to a vibrator (11) made of a magnetostrictive material, thereby generating vending mode vibration. When angular velocity is added to the vibrator (11) in the vibration state, the Coriolis force in the direction orthogonal to the vibration direction is generated in a leg portion of the vibrator (11). In this case, the vibration direction is slightly shifted (twisted) from the basic vibration direction by the Coriolis force. As a result, a stress acting on the leg portion changes, and magnetization caused by an inverse magnetostriction effect also changes. Consequently, in the angular velocity sensor, by detecting a change in the magnetization by detection coils (13a and 13b), the angular velocity applied to the vibrator (11) can be detected in a non-contact manner.
However, since the vibration mode used in the angular velocity sensor (the vibration mode of making the vibrator (11) vending mode vibrate) is a vibration mode which is easily influenced by external vibration, the angular velocity sensor has a problem such that it is difficult to detect the angular velocity with high precision.
As described above, conventionally, various angular velocity sensors have been developed. In the angular velocity sensors disclosed in Japanese Patent Laid-open Nos. Hei 5-1917 and Hei 7-20140, since the vibrator is easily influenced by the external vibration, a problem that it is difficult to detect the angular velocity with high precision exists. The gyro disclosed in Japanese Patent Laid-open No. Hei 10-267667 has a problem such that, although the influence of external vibration on the vibrator can be reduced, the manufacturing cost is very high.